Flood modeling and simulations using hydrodynamic model and ASTER DEM—A case study of Kalpani River

Abstract

The study was conducted to model a 30-km section of the Kalpani River for flood inundation forecasting with the help of remote sensing, geographical information system (GIS), HEC-RAS (1D), and HEC-Geo RAS. 3D coordinates were extracted from ASTER 30 m digital elevation model (DEM). Model was simulated and calibrated for flood 2010 event of 1901 m³ s⁻¹ (upstream) and 3361 m³ s⁻¹ (downstream) on two parameters, i.e., contraction and expansion coefficients and Manning’s “n” values derived from the landuse map of the study area with the known water surface boundary condition. The average difference between known and computed water surface for model’s pre-calibration was 0.64 m, which was reduced in calibration up to 0.11 m. Calibrated model was then validated for flood 2006 event with known discharges, i.e., 1951 m³ s⁻¹ (upstream) and 2285 m³ s⁻¹ (downstream) with an average difference of 0.10 m between known and computed water surface. Calibrated model was further simulated with critical depth boundary conditions instead of known water surface boundary condition, which confirmed the earlier results of the same study. The model results revealed that the Kalpani River, passing through a flat topography of Mardan, with an average slope of 0.000786 m m⁻¹ had a strong positive correlation coefficient of R ² 0.999 and 0.996 between the known and computed water surfaces for calibration and validation, respectively. Finally, the model was simulated for 5-, 10-, 20-, 50- and 100-year return periods with critical depth boundary condition. The risk maps of the study could not be produced owing to the coarser resolution of the DEM followed by area flatness, and river width flood inundation risk factors. It is therefore, suggested that the HEC-RAS model can be used for flood risk management and as decision support tool in the Kalpani River catchment.